Fix typo in MKIT_STUB_README.md

src/stub

             echo " 1. Look for placeholders starting with \`MKIT_STUB_\`"
             echo "    prefix by calling this command:"
             echo ""
-            echo "        grep -lw MKIT_STUB_ -r"
+            echo "        grep -l MKIT_STUB_ -r"
             echo ""
             echo " 2. Go through each file and locate the placeholder.  (You"
             echo "    will also see placeholders like \`__MKIT_*__\`, you can"